1. Field of the Invention
The present invention relates generally to an information terminal that communicates over a dielectric medium, and more particularly, to a receiving apparatus for processing analog baseband signals.
2. Description of the Related Art
Electric-field communication may transfer data using a dielectric, e.g. air, water or the human body, as a transmission medium, to provide intuitive convenience and high security because data is transmitted after a user intuitively selects terminal devices.
FIG. 1 illustrates a Radio Frequency (RF) receiving apparatus used in a conventional RF communication system.
In order to receive RF signals, the RF receiving apparatus should include components related to RF carrier signals, such as a Local Oscillator (LO), quadrature mixer, and Phase Locked Loop (PLL). The RF receiving apparatus should separate a received RF signal into an in-phase signal and a quadrature-phase signal, and convert an analog signal into a digital signal.
FIG. 2 illustrates a conventional broadband pulse signal receiving apparatus.
The broadband pulse signal receiving apparatus illustrated in FIG. 2 is configured to perform electric-field communication only with analog baseband signals, without using RF demodulation.
To restore a weak broadband pulse signal output from a communication channel that uses a human body as a transmission medium to a digital signal, the broadband pulse signal receiving apparatus requires 50-Ohm impedance matching, broadband amplification, and a symmetrical threshold triggering block.
FIG. 3 illustrates an apparatus for receiving an analog baseband differential signal modulated by Amplitude Shift Keying (ASK) in a conventional electric-field communication system.
The receiving apparatus of FIG. 3 uses two electrodes to receive differential signals. For ASK demodulation, the receiving apparatus uses a differential amplifier and a Band-Pass Filter (BPF) that passes only the carrier frequency band signal, and then amplifies the received signal using a peak/hold circuit. Thereafter, the receiving apparatus removes the remaining carrier signal with a Low-Pass Filter (LPF), and then restores the carrier-removed signal to a digital signal using a comparator.
However, the high-frequency band RF receiving apparatus in FIG. 1 requires components (e.g., LO, PLL and quadrature mixers) for processing an RF carrier signal, and components (e.g., a pair of Variable Gain Amplifiers (VGAs), LPFs, and Analog Digital Converters (ADCs)) for processing both an in-phase signal and a quadrature-phase signal, causing an increase in power consumption and space. If a direct conversion structure is used for the LO, DC offset or I/Q mismatch problems may occur.
In the electric-field communication system that employs the analog baseband transmission scheme of FIG. 2, an amplifier having a bandwidth of 100 MHz or more is required to receive broadband pulse signals. This communication system is vulnerable to noise, i.e. interference, from signals out of the reception band since it lacks a filter. In addition, since the communication system utilizes a bandwidth of 100 MHz or more, it may be affected by in-phase RFID signals, such as smartcard operating at 13.56 MHz, or by FM radio signals between about 88 MHz to 108 MHz, causing degradation of performance.
The receiving structure of FIG. 3 is configured to receive analog baseband signals modulated only by ASK, and has two receiving electrodes, which increases installation complexity.